Recently, in the field of magnetic disk devices represented by a hard disk drive, a high-frequency assist recording system has been proposed as one recording system that can realize a higher recording density and a higher recording capacity.
The high-frequency assist recording system is a technique of applying, to a particular minute region in the write signal frequency area of a magnetic recording medium, such as a magnetic disk, a sufficiently high-frequency magnetic field compared to a write signal frequency, using a recording magnetic pole (main pole) that generates a magnetic field when a recording current is applied thereto, and a magnetic head having a high-frequency oscillator, thereby reducing the coercive force of the minute region to half or less than its original coercive force. The high-frequency oscillator is, for example, a spin torque oscillator (STO).
The magnetic disk devices employing the high-frequency assist recording system comprise, near the recording magnetic pole, a spin torque oscillator having an oscillation layer that oscillates when a current is supplied thereto. In these magnetic disk devices, a high-frequency magnetic field generated by the oscillation layer that has oscillated when a current is supplied to the spin torque oscillator is applied to a particular minute portion of the magnetic disk to reduce the coercive force of this portion. At this time, a recording magnetic field is applied by the recorder magnetic pole to the coercive-force reduced portion, thereby recording data on the portion of high magnetic anisotropic energy having a higher density recording potential than a normal magnetic disk.
In the spin torque oscillator of the above-mentioned magnetic head, the oscillation layer is provided near the recorder magnetic pole. A leak recording magnetic field from the recording magnetic pole is applied to the oscillation layer, which varies the recording magnetic field, and hence varies a gap magnetic field applied to the spin torque oscillator. That is, the oscillation frequency of the spin torque oscillator may change. This makes it difficult to realize stable high-frequency assist recording.